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Hercules Clusters II

May 6, 2010

In our region of the galaxy, stars have lots of elbow room -- our nearest neighbor is four light-years away. But there are other neighborhoods in which the stars are separated by mere light-months or even -weeks. And they've been that way since close to the beginning of time.

These neighborhoods are known as globular clusters, and two of them are in good view in the constellation Hercules -- M13 and M92. They're in the northeast as the sky gets good and dark.

Each of them is a ball of hundreds of thousands of stars, yet is only a few dozen light-years across. So each star in the cluster has lots of close neighbors.

All of these neighbors are old and sedate, though. The clusters are probably around 13 billion years old, so their stars were born within a billion years of the Big Bang. Any star that's that old has to be less massive than the Sun, which means it's also fainter than the Sun. Such stars are also cooler than the Sun, so they shine yellow, orange, or red.

Many of the stars are so small and faint that they'd need to be quite close to be visible from any of their neighbors. Even so, with so many neighbors, the skies of any planet in these clusters is likely to be ablaze with stars -- thousands of bright, colorful dots strewn across the firmament.

Under clear, dark skies, M13 is just visible to the unaided eye. M92 is fainter, so you need binoculars or a telescope to pick out this old and crowded stellar neighborhood.

Script by Damond Benningfield, Copyright 2010

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